This dataset summarises benthic surveys of seagrass for Dugong and Turtle habitats in the North-West Torres Strait for November
2015 and January 2016. The Site data describes seagrass at 853 sites; while the Meadow data describes seagrass at 34 individual
meadows. The data includes information on seagrass species, biomass, diversity, and BMI and algae percent cover. The dataset
is available as shapefiles, GIS layer packages, and/or a CSV file.

Methods:

The sampling methods used to study, describe and monitor seagrass meadows were developed by the TropWATER Seagrass Group
and tailored to the location and habitat surveyed; these are described in detail in the relevant publications (https://research.jcu.edu.au/tropwater).

1. Location - Latitude and longitude was recorded by GPS at each site. Depth was recorded when sampling by boat and converted
to depth below mean sea level (dbMSL) in metres.

2 Seagrass metrics - Above-ground biomass was determined using a “visual estimates of biomass” technique (Mellors, 1991)
using trained observers. A linear regression was calculated for the relationship between the observer ranks and the harvested
values. This regression was used to calculate above-ground biomass for all estimated ranks made from the survey sites. Biomass
ranks were then converted into above-ground biomass estimates in grams dry weight per square metre (gdw m-2). Observers
ranked seagrass biomass, and the percent contribution of each species to that biomass, using video transects, grabs, free
divers, and helicopter:

* Video transect: Commonly used for subtidal meadows sampled from larger boats. At each transect site an underwater CCTV
camera system was lowered from the vessel to the bottom. For each transect the camera was towed at drift speed (less than
one knot) for approximately 100m. Footage was observed on a TV monitor and digitally recorded. The video was paused at ten
random time frames and an observer ranked seagrass biomass and species composition. On completion of the video analysis,
the video observer ranked five additional quadrats that had been previously videoed for calibration. These quadrats were
videoed in front of a stationary camera, then harvested, dried and weighed.

* Helicopter: Commonly used for intertidal surveys. At each site seagrass above-ground biomass and species composition were
estimated from three 0.25 m2 quadrats placed randomly within a 10m2 circular area. Seagrass percent cover and sediment type
were recorded at each site. The “visual estimates of biomass” technique when applied to helicopter surveys (and free diving/camera
drops – see below) involves ranking while referring to a series of quadrat photographs of similar seagrass habitats for
which the above-ground biomass has previously been measured. Three separate biomass scales were used: low-biomass, high-biomass,
and Enhalus-biomass. The relative proportion (percentage) of the above-ground biomass of each seagrass species within each
survey quadrat was also recorded. Field biomass ranks were converted into above-ground biomass estimates in grams dry weight
per square metre (gdw m-2). At the completion of sampling each observer ranked a series of calibration quadrats as per video
transect surveys.

* Camera drop/free diving: Commonly used for shallow subtidal meadows sampled from a small boat. Sampling follows the same
protocol as helicopter surveys but the three quadrats were either assessed by a free diver with quadrat, or by an underwater
CCTV camera system camera attached to a frame. Video footage was observed on a TV monitor and seagrass ranked in real time,
with the camera frame serving as a quadrat.

* van Veen grab: Commonly used for shallow subtidal meadows sampled from a small boat in conjunction with camera drops,
or to record seagrass presence/absence where visibility was too poor for camera drops. A sample of seagrass was collected
using a van Veen grab (grab area 0.0625 m2) to identify species present at each site. Species identified from the grab sample
were used to inform species composition assessments made from the video drops (Kuo et al., 1989).

3 Benthic macro-invertebrates - A visual estimate of benthic macro-invertebrate (BMI) percent cover was recorded at each
shallow subtidal and intertidal site according to four broad taxonomic groups:

* Other BMI – Any other BMI identified, e.g. hydroids, ascidians, barnacles, oysters, molluscs. Other BMI are listed in
the “comments” column of the GIS site layer.

4 Algae - A visual estimate of algae percent cover was recorded at each shallow subtidal and intertidal site. When present,
algae were categorised into five functional groups and the percent contribution of each functional group was estimated:

* Erect macrophytes – Macrophytic algae with an erect growth form and high level of cellular differentiation, e.g. Sargassum,
Caulerpa and Galaxaura species.

This layer is presented as three (3) alternate layer packages, including interpolation layers which were created using
site data and meadow boundaries to describe spatial variation in biomass, species diversity and depth gradients. The layers
are:

* "Torres Strait Shannon Weaver diversity interpolation NESP 2015.lpk" - An inverse distance weighted interpolation (IDW)
was applied to seagrass site data to describe spatial variation in seagrass species diversity across each meadow and throughout
the north-west Torres Strait region. The Shannon-Weaver index is a mathematical measure of species diversity that uses species
richness (the number of species present, where a score of 0 = one species present) and the relative abundance of different
species (Spellerberg et al., 2003).

* Seagrass community types were determined according to species composition within a meadow. Species composition was based
on the percent each species’ biomass contributed to mean meadow biomass. A standard nomenclature system was used to categorize
each meadow (see Table 1 "Nomenclature for seagrass community types" in final report). This nomenclature also included a
measure of meadow density categories (light, moderate, dense) determined by mean biomass of the dominant species within
the meadow (see Table 2 "Density categories and mean above-ground biomass ranges for each species used in determining seagrass
community density" in final report).

* Mapping precision estimates (in metres) were based on the mapping method used for that meadow (Table 3 "Mapping precision
and methods for seagrass meadows" in final report). Mapping precision estimates ranged from 1-10m for intertidal seagrass
meadows to >100m for patchy subtidal meadows. Subtidal meadow mapping precision estimates were based on the distance between
sites with and without seagrass. The mapping precision estimate was used to calculate an error buffer around each meadow;
the area of this buffer is expressed as a meadow reliability estimate (R) in hectares.

Spellerberg, I. F., & Fedor, P. J. (2003). A tribute to Claude Shannon (1916–2001) and a plea for more rigorous use of species
richness, species diversity and the ‘Shannon–Wiener’ Index. Global Ecology and Biogeography, 12(3), 177-179.

Data Location:

This dataset is saved in the eAtlas enduring data repository at: data\NESP1\3.5_North-West-TS_Seagrass

Point of contact

Individual name

Carter, Alex, Dr

Organisation name

TropWATER, James Cook University (JCU)

Role

pointOfContact: party who can be contacted for acquiring knowledge about or acquisition of the resource